The invention is in the field of devices used in the processing of semiconductor wafers. More particularly, the invention relates to a cantilever paddle used to position semiconductor wafer boats within processing furnaces and other processing systems.
During processing, semiconductor wafers must often be heated within specialized furnaces. Such furnaces typically comprise elongated, cylindrical tubes. Likewise, wafers may be subjected to other processing steps, such as low pressure chemical vapor deposition, within reactors which also comprise elongated, cylindrical tubes. Wafers are positioned within the furnaces and reactors in a manner such that they are aligned along planes defined by circular cross-sections of the furnace or reactor and are spaced at predetermined, generally equidistant, points along the central axis of the furnace or reactor.
In order to achieve the desired positioning and spacing within the processing chambers, the wafers are commonly positioned in slotted holders, called wafer boats, or simply boats, which stand the wafers in a spaced configuration aligned along a central axis. In order to survive the processing conditions within the chamber, and to minimize chemical contributions to the wafers from the processing equipment, the boats and many other devices used in wafer processing are fabricated of a material such as silicon carbide (SiC).
The boats, loaded with a batch of wafers to be processed, are positioned on long cantilevered paddles, by which they may be inserted into and withdrawn from the tubular furnaces and reactors. Such paddles typically include a flattened carrier section upon which one or more boats may be positioned, and a long handle, positioned at one end of the flattened carrier section, by which the paddle can be handled. When the paddle is formed as a monolithic body, a transition section is typically formed between the handle and the carrier section. Of course, the handle must extend out of the furnace or reactor to allow it and the wafer boats to be manipulated.
Positioning of the wafer boats within the furnace or reactor is important, because to provide uniformity to the processing conditions to which the wafers will be subjected, it is desirable to position the center of each wafer as close to the central axis of the furnace or reactor as possible. Thus, bending of the paddle caused by the weight of the wafer-loaded boats must be considered in paddle designs, particularly because the paddle is supported only at one end, i.e., the end that extends from the chamber. Along with considerations of paddle design resulting from operating weight requirements, a set of clamps designed to precisely hold the extending end of the paddle in position must be used. These clamps must be considerably robust to maintain the paddle at a precise desired position, while at the same time being simple to use and minimizing the possibility of paddle damage during clamping.
Recently, manufacturers of semiconductor wafers have sought to use furnaces and reactors capable of processing greater number of wafers. Unfortunately, existing paddles cannot handle the increased weight loading of additional wafers and wafer boats. These additional weight loads cause the paddles to deflect or bend too far downward, causing them to contact the underlying chamber wall and become stuck. Although paddles with thicker handles have been proposed, early tests of these designs show that they are also unsuitable. In particular, when heavier paddles are used with lighter loads, they do not deflect enough. As a result, the mounted wafers often contact the upper wall of the furnace or reactor interior and become broken or damaged. Likewise, heavier paddles are formed using heavier handles, and such handles are not compatible with the existing clamps. Providing new clamps to secure the heavier handled paddles would be a significant economic burden.
The prior art discloses paddles or transfer jigs for use in semiconductor wafer processing. However, unlike the present invention, the prior art does not address nor overcome the disadvantages noted hereinabove. For example, in JP314637, there is disclosed a quartz glass transfer jig for a wafer boat which purports to decrease deflection without increasing the thickness of the entire jig. The jig, however, is strengthened by the provision of a reinforcement member.
JP1251713 recites that the wall of a fixed portion of a quartz glass wafer boat holding section is made thicker than that of other portions thereof by a predetermined range above a central axis in order to reduce bending stress and increase rigidity.
Thus, a need exists for a cantilever paddle that can be used with a heavier weight burden, while at the same time remaining compatible with existing clamp systems. A need also exists for a cantilever paddle that exhibits acceptable deflection characteristics over the entire range of weight loads with which it may be used.
The present invention relates to a cantilever paddle that is configured to address the problems now being encountered with prior art paddle designs. More specifically, the present invention relates to a cantilever paddle for use in semiconductor wafer processing that exhibits acceptable deflection characteristics over the entire range of weight loads with which it may be used, and that is compatible with existing clamp systems.
The inventive paddle is characterized in that it employs a handle portion configured to reduce deflection while also remaining compatible with current clamps. This is achieved by providing a xe2x80x9ctwo-stagexe2x80x9d handle having a large diameter section and a small diameter section, the sections being separated by a handle transition zone. Of course the paddle also includes a carrier section connected to the handle through a carrier transition zone.
The desirable characteristics of the two-stage handle result from one or more design parameters discussed in detail below.